Hexadecimal integers are commonly used in programming environments because each hexadecimal digit represents four binary bits. A hexadecimal number is any sequence of these digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D,E, F. The integers are called hexadecimal because they are based on 16 different digits. Case sensitivity rules do not apply to numbers, so you can use
lowercase letters as well. The prefix for hexadecimal numbers is 0x or 0X. Hexadecimal numbers might look familiar to HTML authors. In early versions of Netscape Navigator and Internet Explorer, colors were specified in a hexadecimal triplet format. Although the latest versions of Netscape Navigator and Internet Explorer let you specify colors by their names, some people continue to use the hexadecimal notation. The following tag sets the background color to the default gray (even for users who changed their default to white):